Add Xbox controller diagnostics

[okch-codes]

Summary

• add Xbox/XInput detection and live input through the browser Gamepad API
• add an Xbox-specific controller diagram with sticks, triggers, D-pad, and button visualization
• integrate Xbox button diagnostics into Quick Test while excluding OS-reserved Guide and unreliable browser vibration tests
• add an Xbox Accessories handoff for permanent calibration
• improve the Xbox connection modal, cancellation, timeout, and spinner behavior
• update documentation, metadata, and automated Xbox mapping tests

Testing

• npm test
• npm run build:prod

Xbox firmware calibration remains outside the browser because the Gamepad API does not expose calibration writes.

[carpikes]

Hi, thank you for this PR! Will review it in these days and merge it.

[carpikes]

Great work! I'm currently reviewing it, but I think the PR is much larger than it needs to be.

I would recommend splitting it into a few smaller, self-contained PRs.
That makes the review process much easier and helps keep each change focused.

For example, the first PR could simply add basic Xbox controller support (e.g. connection) while keeping all the buttons disabled and avoiding text/UI renames. Then other improvements could follow in separate PRs.

One more thing: I noticed this PR renames the project from "DualShock Calibration GUI" to "Controller Calibration GUI".
For now, I'd prefer to keep the existing name unchanged and leave that discussion for a separate PR if we decide to rebrand it later.

Thank you!

EDIT: Just added a CONTRIBUTING.md with guidelines on how to contribute.
https://github.com/dualshock-tools/dualshock-tools.github.io/blob/main/CONTRIBUTING.md